Optical design for the distribution of electromagnetic radiation is generally broken down into two principal fields, imaging and non-imaging optics. (In this specification, “light” and “optical” comprise portions of the electromagnetic spectrum which include the visible spectrum and which may lie outside of the visible spectrum.) The field of imaging optics can be defined as the science of transferring electromagnetic energy from an object plane to an image plane with minimal distortion. The “object plane” or “input image” can be defined as a predetermined energy input distribution, while the “image plane” or “output image” can be defined as a predetermined energy output distribution which may vary in both intensity and direction.
Typically, imaging optical systems significantly attenuate the input image energy in the process of minimizing the output image's distortion. The degree to which the imaging optical system attenuates the energy transfer depends upon the application. However, in most instances there is a significant loss of electromagnetic energy by the time it reaches the image plane. This degree of energy attenuation is acceptable for applications, such as cameras, microscopes and the like. In contrast, when the application is an illumination system, the primary goal is to maximize the energy throughput of the optical system. Hence, the other field of optical design, non-imaging optics, is the science of maximizing the transfer of electromagnetic energy from a source image to an output image or from an object plane to an image plane.
There are many situations where electromagnetic energy is required to be distributed into a pre-determined output image and a high transfer of source energy is desirable. For example, overland vehicle safety lighting, aircraft lighting, street lamp lighting and marine lighting require specific output patterns determined by government regulations which can have minimum and maximum illumination values and which vary substantially in different directions. In each case, regulations typically specify minimal photometric requirements which must be met by the device. There are other applications where it would be desirable to project a highly even illumination onto a flat or complex surface or surfaces. This type of illumination would be very useful for many industrial purposes, but in the past, has been difficult or impossible to achieve.
The field of non-imaging optics has historically been confined to optics which, by definition, could not generate images. In past non-imaging solutions, designers used simplified surface geometry to approximate a desired output distribution resulting in non-optimal solutions which necessitated greater source energy and higher system power requirements. One common design technique associated with these solutions is to first collimate the source energy using a surface or multiple surfaces to form a relatively narrow angular output distribution and then re-distribute the collimated energy using a second output surface. Output surfaces in these typical collimated light solutions are comprised of a few simple shapes including ellipses, parabolas, radii, torroidal sections, multiple radii surfaces and swept or extruded combinations thereof.
By way of example FIG. 1 shows, in table form, a combination of various output values for SAE/DOT regulations for a stop turn tail lamp. As illustrated, the “output image” varies in both intensity and direction. Historically, the preferred energy source for these stop turn tail lamp devices was an incandescent lamp. Recent advances in technology have allowed light emitting diodes (LED's) to be employed as the source energy. LED's have many advantages over incandescent sources including; longer life, faster turn on times and lower energy consumption. The main disadvantage of LED sources is the cost which can be 10 times that of an incandescent lamp. The cost associated with these improved sources combined with the difficulty in achieving appropriate energy distribution when simplified optical geometries are employed, can make the use of LEDs cost prohibitive in many real world situations.